function [dist2Handle] = dist2HandleFactory(name)
% Generates the distance handle object on postivie reals for Hilbertian metric
% dist2Handle = dist2HandleFactory(name)
% Input:
%   name: (string) Name of the 1/2-homogeneous metric
%          Valid values: MSC, JS, Total-variation, Hellinger
% Output:
%   sigma: (@) function handle for the metric
%
% References
% [1] Matthias Hein, Olivier Bousquet. "Hilbertian Metrics and Positive Definite
%   Kernels on Probability Measures" In AISTATS (2005)
%
% $Id: dist2HandleFactory.m 26 2010-02-06 19:40:58Z memming $
% Copyright 2009 iocane project. All rights reserved.

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%    this list of conditions and the following disclaimer in the documentation
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%  - Neither the name of the iocane project nor the names of its contributors
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%
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switch lower(name)
case {'mean square difference', 'msd', 'msc', 'chi-square'}
    dist2Handle = @(p,q)( (p-q)^2 / (p+q) );
case {'hellinger'} % Hellinger
    dist2Handle = @(p,q)( (sqrt(p) - sqrt(q))^2 );
case {'js', 'jensen-shannon'}
    dist2Handle = @(p,q)( 1/log(2) * ...
	(p * log(2 * p/ (p+q)) + q * log(2 * q/ (p+q))) );
case {'total variation'}
    dist2Handle = @(p,q)( abs(p - q) );
otherwise
    error('Unknown R+ metric [%s]', name);
end
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